The luxury group shot back Tuesday by revealing it would file a suit against Hermès for “slander, blackmail and unfair competition.”

Hermès International and LVMH Moët Hennessy Louis Vuitton said Tuesday they were heading to court over their ongoing dispute regarding LVMH’s acquisition of a 22.3 percent stake in the maker of Birkin bags and silk scarves.

The world’s biggest luxury group has since steadily increased its stake, a move seen by Hermès officials as an attempt at a creeping takeover, despite reassurances from LVMH chairman and chief executive officer Bernard Arnault that he is not seeking full control.

“This complaint concerns the terms of LVMH’s acquisition of stock in Hermès International,” Hermès said in a two-line statement. It is accusing LVMH of insider trading, collusion and manipulating stock prices, according to a source familiar with the issue, who declined to be named for confidentiality reasons.

A spokeswoman for the Paris prosecutor’s office said the court was examining the complaint and had referred the matter for opinion to the stock market regulator AMF, which in November 2010 launched an investigation to determine if LVMH respected market rules. That inquiry is still open.

LVMH shot back Tuesday by revealing it would file a suit against Hermès for “slander, blackmail and unfair competition.”

“By filing its complaint, Hermès seeks to bypass the appropriate AMF channels without waiting for the result of the official enquiry [sic] and without determining the extent of the AMF’s findings to date. In addition, the filing carries serious and unfounded accusations about market failings,” LVMH said.

The luxury conglomerate said it awaited the results of the probe “with complete peace of mind” and was confident the AMF would find it did no wrong.

“LVMH has no doubt that the inquiry will determine that the Hermès allegations are false and serve no other purpose than to slander and unlawfully undermine another firm in the same industry,” it said.

The war of words between Hermès and LVMH, which reached a paroxysm in the months following Arnault’s initial move, appeared to have died down in the last 12 months as Hermès battened down the hatches with a series of measures designed to lock out any unwanted shareholders.

Last year, the Court of Appeal in Paris handed Hermès a major victory by authorizing it to group family-owned shares into a nonlisted holding company.

The Dumas, Puech and Guerrand families collectively own more than 70 percent of the shares in Hermès International, a limited partnership structure that guarantees they keep control of management.

The H51 holding company, completed in December, groups 50.2 percent of the company’s capital and has priority purchasing rights on the remaining shares held by the family members participating in the initiative — some 12.6 percent of capital.

A notable holdout was Nicolas Puech, the single-largest family shareholder, who has so far withheld his 5.8 percent of the capital from the holding company. But in a symbolic move signaling family unity, shareholders gathered at the firm’s annual general meeting in May approved his nomination to the supervisory board.

At the same meeting, they green-lighted a change in statutes requiring holders of more than 0.5 percent of shares to register them to their name — another move apparently designed to prevent any stealthy acquisitions by LVMH.

Hermès chief operating officer Axel Dumas, who will be named joint ceo alongside Patrick Thomas in June 2013 under a gradual succession plan, said he planned to uphold the family’s hostile stance toward LVMH and Arnault.

“Our policy will remain unchanged,” he told reporters on the sidelines of the annual meeting.

But in recent months, Hermès officials have fallen silent about the spat, making Tuesday’s announcement all the more unexpected.

The case is likely to remain at a standstill until the AMF publishes the results of its probe into the LVMH acquisition of Hermès shares, at an as-yet-undetermined date.

The stock market regulator said in June it had launched a public consultation on plans to change its rules so that cash-settled equity swaps would in the future be taken into account when declaring share purchases that cross given thresholds.

Officials at AMF were not available at press time Tuesday to confirm when the results of the consultation, which ran until Aug. 6, would be made public, and whether they would affect the completion of its probe into LVMH.

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